As histone proteins bind DNA prior to transcription, their biochemical action plays a critical role in the regulation of gene expression and cellular differentiation. Histone deacetylases (HDACs) are an important family of proteins predominantly responsible for specific posttranslational modifications of histone proteins, the chief organizational component of chromatin. HDACs catalyze the removal of acetyl groups from histones and other cellular proteins. HDAC-mediated deacetylation of chromatin-bound histones regulates the expression of a variety of genes throughout the genome. Importantly, HDACs have been linked to cancer, as well as other health conditions. To date, eleven major HDAC isoforms have been described (HDACs 1-11). HDACs are categorized into two classes. Class I HDACs include HDAC1, HDAC2, HDAC3, HDAC8 and HDAC11. Class II HDACs include HDAC4, HDAC5, HDAC6, HDAC7, HDAC9 and HDAC10. HDAC's are validated targets for a number of disease states, including cancer, neurodegenerative diseases, sickle-cell anemia, muscular dystrophy, and HIV. There are currently two HDAC inhibitors on the market, Vorniostat and Romidepsin. Both are approved for treatment of T-cell lymphoma. However, they are both pan active inhibitors showing very little specificity of binding to HDAC subclasses. Because of this lack of specificity they have a number of side effects.
Non-selective HDAC inhibitors effect deacetylase activity of most, if not all, of the HDACs. The mechanisms of the anticancer effects of SAHA, a non-selective HDAC inhibitor, are not completely understood, and likely result from both altered gene expression and altered function of proteins regulating cell proliferation and cell death pathways. Non-selective HDAC inhibitors, such as SAHA, induce the accumulation of acetylated histone proteins and non histone proteins.
Small molecule HDAC inhibitors that are isoform-selective are useful as therapeutic agents with reduced toxicity and as tools for probing the biology of the HDAC isoforms. The present disclosure is related, in part to small molecules that are selective HDAC inhibitors.